The ultimate goal of this research is to produce a "high fidelity" hearing aid as perceived by the hearing impaired user. This is the final phase of a research program started by the writer in the 1970's in an attempt to determine the design requirements for a high fidelity hearing aid for what should be the simplest case: individuals with a hearing loss characterized by a mild to moderate loss of sensitivity for quiet sounds but normal or near-normal hearing for loud sounds. Available evidence indicates that such individuals may constitute a large proportion of the hearing impaired who do not now wear hearing aids, and thus the market for a successful design appears conceivably greater than the entire present hearing aid market. In order to determine what proportion of these non-wearers might purchase a hearing aid if it involved no auditory disadvantages, a hearing aid without the current electroacoustic limitations needs to be made available. In the writer's judgement, the only remaining component needed to make such a hearing aid is a low distortion four-stage compression amplifier with level dependent high frequency emphasis. Such an amplifier, to be made available to the hearing aid industry, is the direct goal of the present application.